In composite materials, the most common types of fiber are glass, aramid, or carbon. If the highest stiffness per weight is desired, then a design engineer might choose carbon. Aramid is an excellent choice for impact resistance, having the greatest strength per unit of weight. If cost is the main concern, fiberglass will give the greatest strength per dollar.
"Of course, there are many other factors used in selecting a type of fiber," notes Greg Kress of Kress Precision Composites (Pensacola, FL). "Even among these categories of fibers there is a wide range of stiffness values for carbon, several for aramid, and different types of glass fiber. Less commonly used reinforcement fibers are polyethylene (AlliedSignal Spectra®) and boron, which have unique properties that may make them the best material for the job."
Keep in mind, however, reinforcement fibers hold the key to strength in any composite structure. A composite fabricator normally has several types of fibers to choose from, as well as pages and pages of weave styles. Before an accurate selection can be made for the best reinforcement, the engineer needs to know more about the terminology used to completely describe how reinforcement fibers are presented. Any major fiber maker or composite manufacturer can lend an assist.